A quaternary ammonium salt manifesting liquid condition at ordinary temperature (25° C.) is paid attention to as an organic synthesis reaction solvent (see, T. Welton, Chem. Rev., 99, 2071-2083 (1999)). As described in the above-mentioned literature, a quaternary ammonium salt such as an ethylmethylimidazolium salt and the like can be used as a reaction solvent capable of being utilized repeatedly and is paid attention to as a novel solvent giving low environmental load also from the standpoint of green chemistry, because of properties such as that the salt has extremely low volatility, is thermally stable and capable of standing a reaction at higher temperatures, that the salt is chemically stable, further that the salt shows high solubility for various organic compounds, and the like. Furthermore, application thereof as an electrolyte for organic electrolytic synthesis is expected, because of properties such as ion conductivity, electrochemical stability and the like. As the quaternary ammonium salts showing liquid condition at room temperature, for example, an N-butyl-N-methylpiperidinium salt, N-butyl-N-methylpyrrolidinium salt and the like are mentioned, and as the anion thereof, there are known a bis(trifluoromethylsulfonyl)imidate ion [N(SO2CF3)2−], tetrafluoroborate ion (BF4−), hexafluorophosphate ion (PF6−) and the like.
In such applications, from the standpoint of promotion of the reaction by the means of stirring load or substance transfer, there has been a desire for development of a quaternary ammonium salt of lower viscosity.